Method for manufacturing a component interconnect board

ABSTRACT

There is provided a method for manufacturing a component interconnect board ( 150 ) comprising a conductor structure for providing electrical circuitry to at least one component ( 114 ) when mounted on the component board, the method comprising providing a conductor sheet ( 100 ) with a first predetermined pattern ( 115 ), providing a solder resist sheet ( 112 ) with a second predetermined pattern for defining solder areas ( 125 ) of the component board, forming a subassembly ( 120 ) by laminating the solder resist sheet on top of the conductor sheet, applying solder onto the subassembly, placing the at least one component onto the subassembly, performing soldering, and laminating the subassembly to a substrate ( 130 ). The solder resist sheet is further arranged to act as a carrier for the conductor sheet.

TECHNICAL FIELD

The present invention generally relates to the field of light emittingdiode luminaires, and more particularly to a method for manufacturing acomponent interconnect board for light emitting diode luminaires.

BACKGROUND OF THE INVENTION

In the cost breakdown of light emitting diode (LED) luminaires, thecomponent to circuitry interconnect solution, or when the component ispart of the circuitry, herein under referred to as a level two (L2)interconnect, is becoming increasingly important because of two mainreasons. Firstly, the LED costs are decreasing, and secondly, in manyLED luminaire designs, there is little room left to have a cost down onfor example the housing parts. Both reasons lead to a relative increaseof importance of the L2 interconnect on the total system costs.

FIG. 1 schematically illustrates a typical L2 interconnect in which acomponent, here a packaged LED 10, is interconnected with a LED board 50being a printed circuit board, PCB, by means of soldering. A LED boardis usually provided as a stack. The LED board 50 comprises a carryingsubstrate 51 for providing a required robustness, or flexibility, of theLED board 50. One or more dielectric layers 55 for providing a basicinsulation of the LED board 50 is typically laminated together withepoxy resin onto the substrate 51. On top of the substrate 51, aconductor layer is also laminated over the full surface area. Theconductor layer is thereafter chemically etched to provide for the finalconductor structure 52 and circuitry. This etching process is by naturea discontinuous batch process. The LED 10 is interconnected to theconductor structure 52 by means of soldering. Before applying solder 53to the LED board it is typically coated with a solder mask, a patternedsolder resist layer 54, defining areas where solder is to be applied.The solder resist layer 54, which is typically 20-30 micrometers thick,may be a polymer coating applied in an offset process of a dispensed andcured polymer material. The solder resist layer 54 prevents solder frombridging between conductors 52 thereby creating short circuits, and mayfurther provide protection from the environment.

Whereas the whole stack of a PCB is typically produced by lamination,the actual final end result for the conductor circuitry 52 and solderresist 54 is created by a discontinuous process. These batch processesdo not come down in cost significantly with larger volumes inproduction.

Further, with respect to material utilization, there is littleflexibility in playing with the essential and valuable conductor layerproperties. When providing the conductor structure 52, firstly a copperlayer is applied to the full L2 process plate surface, followed bypatterning and removing of copper, which cost time and saturates thechemical etching dissolvent. Growing a thicker layer, for better heatmanagement, also cost extra time and energy.

In addition to the standard PCB type of L2 interconnect described above,there are many other types of L2 interconnects, which are mostly notrelevant for reasons of high cost and complexity. One solution that isof relative low cost and which may be used for less complex circuitriesis using lead-frames. In general this means putting components on arigid, possibly bended, conductor frame, which is processed in a finalstage to provide for the required circuitry. The lead-frame can beproduced in different ways depending mostly on size and complexity e.g.mechanical stamping or chemical etching. There are some typicaldrawbacks to this approach. Firstly with creating the final circuitrythe initial lead-frame will lose its mechanical integrity literallyfalling apart. One can either design to have mechanical stresses goingthrough the electrical components such as is typical in largermechanical lead-frames, or one can introduce some feature, e.g. plasticovermoulding, to provide for the necessary rigidity while the finalcircuitry is created before electrical components can be placed.Furthermore in general these types of solutions do not provide for thenecessary electronic insulation requirements whereas dielectrics are notor only applied in limited areas. Prescribed creepage and clearancedistances are difficult to manage or incorporate into the L2interconnect design and must mostly be managed on a luminaire/systemlevel. Finally if one wants to optimize for thermal management and theheat spreader and/or heat sink is made out of conductive material onehas to introduce a separate dielectric component on a luminaire/systemlevel.

SUMMARY OF THE INVENTION

In view of the above, an object of the invention is to at leastalleviate the problems discussed above. In particular, an object is toprovide a method for manufacturing a component interconnect board in amore material efficient, faster and more economical manner.

This object is achieved by a method for manufacturing a componentinterconnect board according to the present invention as defined inclaim 1. The invention is based on the insight that by starting fromsheet based solder resist and conductor materials, and utilizing thesolder resist sheet to function as a carrier for the conductor sheet,mechanical processing can be used in order to make the final circuitry.

Thus, in accordance with an aspect of the present invention, there isprovided a method for manufacturing a component interconnect boardcomprising a conductor structure for providing electrical circuitry toat least one component when mounted on the component board. The methodcomprises providing a conductor sheet with a first predeterminedpattern, providing a solder resist sheet with a second predeterminedpattern for defining solder areas of the component board, forming asubassembly by laminating the solder resist sheet on top of theconductor sheet, applying solder onto the subassembly, placing the atleast one component onto the subassembly, performing soldering, andlaminating the subassembly to a substrate. In the subassembly, thesolder resist sheet is further arranged to act as a carrier for thepatterned conductor sheet, thereby maintaining integrity of thesubassembly, during steps of the manufacturing. The manufacturing andassembling of the circuitry are thus decoupled from the substrate, whichis advantageous in that the substrate can be chosen freely e.g. toprovide for proper thermal dissipation, provide low light leakage fromLEDs mounted on the component interconnect board, or to providecontrollable creepage and clearance distances. Decoupling further allowsseparate processing of the carrier substrate in order to optimize thesubstrate and use its specific mechanical, optical or thermal propertiesto the full extent.

Further, a high utilization factor of high value materials like copperand aluminium is obtainable when providing the conductor structure froma patterned conductor sheet. This is particularly true when onestretches a single circuitry sub assembly, or distributes multiplecircuitry sub assemblies, over a larger substrate, as will be furtherdescribed below.

Due to the use of sheet materials, the present method may be implementedin a roll-to-roll process which is advantageous. Contrary to batchprocesses, which as mentioned above do not come down in costsignificantly with larger volumes in production, continuous processes,like roll-to-roll processes, are very sensitive to economies of scaleand are therefore cost effective for high volume production. In aroll-to-roll process large dimensions of the circuitry are allowed, e.g.infinite length is possible. There is no need for expensive L2interconnect to L2 interconnect connectors on a luminaire/system.

Further, the present inventive method can provide high capacityutilization of machinery, because the subassembly and intermediateproducts can be produced and stocked separately. Every step of themanufacturing method may correspond to its own flexible machine.

Generally the present invention provides for a high freedom in layoutdesign compared to lead-frame type solutions. This is because in thedesign of a lead-frame type of L2 interconnect there is a trade offbetween freedom in circuitry layout and mechanical rigidity/integrity.In the present invention the two different functionalities are managedby two different layers. Furthermore in current PCB type of L2interconnect solutions one can either chose to apply free shaping ofcontours by a relatively expensive milling process step, or one islimited to linear cutting resulting in typical rectangular shapes. Inthe present invention the circuitry assembly is decoupled from thesubstrate which means that designing for a larger or more complex finalassembly does mostly affect the substrate design and materialutilization whereas the more valuable circuitry assembly may remainunchanged.

According to an embodiment of the method, it further comprises cuttingthe subassembly to provide the conductor sheet with a finalpredetermined pattern corresponding to the conductor structure, which isadvantageous if the first predetermined pattern is not corresponding tothe desired conductor structure.

According to embodiments of the method, it further comprises providingmechanical deformation of the subassembly by means of one of splitting,trimming of the subassembly to a predetermined contour, and stretching.For instance, to create large dimensions of the component interconnectboard, it may be advantageous to create the circuitry and do the pickand placing of components first, and subsequently stretch thesubassembly to a desired size before finally transferring it to thesubstrate. Preferably, the conductor structure is provided withextractable conductor portions. The component pick and placing is thenperformed with an as high as possible density, which is advantageous.Preferably, the subassembly comprising the conductor structure withextractable conductor portions is then stretched to an optimized totalsurface area and thickness before putting it on a carrier substrate. Thesubstrate may be a final product or carrier, like for instance aluminaire housing part, an internal or external reflector, glass windowpane, acoustically absorbing foam etc.

The separation of the manufacturing of the circuitry from the substratefurther allows integration of various further functionalities in thesubstrate, like mechanical fixation, optical reflector and electricalconnector before applying the subassembly to the substrate.

According to embodiments of the method, it further comprises providingthree dimensional deformation of the subassembly for providing one of:optical properties, like specular or diffuse reflector, mechanicalfixation of the component interconnect board, e.g. by bending orprotrusions, mechanical fixation of additional components, like near dieoptics or local heat sinks, thermal properties, and connectorfunctionality.

According to embodiments of the invention, the substrate may be isflexible and/or three dimensional.

Further, the substrate may in an embodiment of the method bemechanically deformed. This may be done by one of splitting, andtrimming of the substrate to a predetermined contour.

According to embodiments of the method, it further comprises providingthree dimensional deformation of the substrate for providing one ofoptical properties, like specular or diffuse reflector, mechanicalfixation of the component interconnect board, e.g. by bending orproviding protrusions, mechanical fixation of additional components,like e.g. near die optics or local heatsinks, thermal properties, andconnector functionality. Optionally, the subassembly can incorporatefeatures for providing additional functionalities, such as mounting orpositioning features, such as providing snap fit features, slots orholes for primary optics, increasing the stiffness, e.g. by profiling.

According to an embodiment of the method, the conductor structure isfurther arranged to function as a connector.

According to an embodiment of the method, at least one of the firstpredetermined pattern and the second predetermined pattern is done bymeans of cutting, punching, or slitting.

The described invention is broadly applicable in LED products. For LEDmodules, LED lamps which have a relatively high thermal load to volumeratio it is highly advantageous because the solution can be optimizedfor thermal management while still being low cost. For LED boardplatforms, and large area luminaries in general it is advantageousbecause the solution provides for a novel way to distribute LEDs overlarge surface areas while still being low cost and possibly evenincorporate a luminaire housing functionality.

Other objectives, features and advantages will appear from the followingdetailed disclosure, from the attached dependent claims as well as fromthe drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as additional objects, features and advantages of thepresent invention, will be better understood through the followingillustrative and non-limiting detailed description of preferredembodiments of the present invention, with reference to the appendeddrawings, where the same reference numerals will be used for similarelements, wherein:

FIG. 1 is a cross sectional side view schematically illustrating a priorart L2 interconnect;

FIG. 2 is a flow chart schematically illustrating an embodiment of amethod according to the present invention;

FIG. 3 is a flow chart schematically illustrating an embodiment of amethod according to the present invention; and

FIG. 4 is a schematic illustration of an embodiment of the methodaccording to the present invention when implemented in a roll-to-rollmanufacturing line.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Exemplifying embodiments of the method for manufacturing a componentinterconnect board according to the present invention is now describedwith reference to FIGS. 2, 3 and 4. The steps of the method are shown asa numerical sequence, however some of the steps may be performed inanother order.

With reference now to FIG. 2, and starting at step 1100, a conductorsheet 100 is initially provided. The conductor sheet 100 is preferablyselected amongst a group of metal sheet materials comprising copper andsilver. The conductor sheet 100 is in step 1101 pre-cut to apply a firstpredetermined pattern 115 corresponding to a specific electronic layoutwhile still maintaining the necessary integrity.

In a parallel step 1102, a solder resist sheet 112 is pre-cut to providea second predetermined pattern, here defining openings 125 for definingsolder areas, while still maintaining the necessary integrity.

The maintained integrity of the patterned conductor sheet 111 and thepatterned solder resist sheet 112 is of particularly importance when atleast steps of the method are implemented in a roll-to-roll process,which is described herein under with reference to FIG. 4.

To continue with reference to FIG. 2, the patterned conductor sheet 111and the patterned solder resist sheet 112 is in step 1103 laminated toform a subassembly 120.

In step 1104, solder 113 is applied to cleared areas defined by theopenings 125 in the solder resist sheet 112.

Subsequently, in step 1105, pick and placing of components 114, beingfor instance LEDs, is performed followed by soldering, which may be areflow soldering process, in step 1106. Optionally, if necessary, thesubassembly 120 is in step 1107 cut to provide for a final predeterminedpattern 116 corresponding to the conductor structure, i.e. theelectronic circuitry of the components 114. In step 1108 the subassembly120, now containing both the final circuitry and components 114, issplit (cut) in multiple parts here forming two subassemblies, 120 a and120 b. In a final step 1109, the parts 120 a (not shown) and 120 b ofthe subassembly 120 are laminated to an appropriate substrate 130,taking into account creepage and clearances, resulting in a componentinterconnect board 150. In embodiments of the method, the substrate orthe component interconnect board may be further mechanically deformed toadd functionalities, e.g. mounting features or positioning features forprimary optics.

The mechanical deforming of the subassembly in step 1108 is optional,and can in embodiments of the method comprise trimming of thesubassembly (and/or parts of the subassembly when performing splittingof the subassembly, as described in step 1108 above) to a predeterminedcontour.

FIG. 3 is a flow chart schematically illustrating an embodiment of amethod according to the present invention. Starting at step 1200, aconductor sheet 200 is initially provided. The conductor sheet 200 is instep 1201 pre-cut to apply a first predetermined pattern 215corresponding to a specific electronic layout while still maintainingthe necessary integrity. The first predetermined pattern 215 comprisesof a matrix of m×n component areas, C_(n×m), arranged in n rows and mcolumns, here n=3 and m=3, see for instance connect areas 212 a and 212b, to which components are to be soldered, in the schematic close up ofthe patterned conductor sheet 211, which connect areas 212 a and 212 btogether constitute a component area C_(3,1). Further, substantiallyU-shaped conductor portions 216 are arranged to interconnect adjacentconductor areas C_(n,m). As illustrated in FIG. 3, the conductorportions 216 are cut out from the conductor sheet 200 with maintainedintegrity by keeping a bridge part 217 a.

In a parallel step 1202, a solder resist sheet 212 is pre-cut to providea second predetermined pattern, here comprising covering areas 226,corresponding to each component area C_(n,m) of the patterned conductorsheet 211 in which openings 225 for defining solder areas are arranged.Further, each covering area 226 is interconnected with a bridge 217arranged at positions corresponding to bridge parts 217 a of thepatterned conductor sheet 211.

Maintained integrity of the patterned conductor sheet 211 and thepatterned solder resist sheet 212 is of particularly importance when atleast steps of the method are implemented in a roll-to-roll process,which is described herein under with reference to FIG. 4.

To continue with reference to FIG. 3, in step 1203 the patternedconductor sheet 211 is laminated to the patterned solder resist sheet212 to form a subassembly 220. In step 1204, solder 213 is applied tocleared areas defined by the openings 225. Subsequently, pick andplacing of components 214, being for instance LEDs, in step 1205 isperformed followed by soldering, which may be a reflow solderingprocess, in step 1206.

In step 1207, the subassembly 220 is cut to provide for a finalpredetermined pattern corresponding to the conductor structure, i.e. theelectronic circuitry to the components 214. Here, the part of thebridges 217 a and 217 are simultaneously trimmed, e.g. by punching, suchthat the conductor portions 216 are no longer bridged.

In step 1208 the subassembly 220, now containing both the finalcircuitry and components 214, is mechanically deformed. The matrix ofcomponent areas C_(n×m) is stretched, thereby straightening out theconductor portions 216 such that the distance between the components 214and the L2 interconnect surface area (area of subassembly 220)increases. Here, the stretching is done in two dimensions.

In a final step 1209, the stretched subassembly 220 is laminated to anappropriate substrate 230, taking into account creepage and clearances,resulting in a component interconnect board 250. In embodiments of themethod, the substrate or the component interconnect board may be furthermechanically deformed to add functionalities, e.g. mounting features orpositioning features for primary optics.

According to an embodiment of the method according to the presentinvention, it is implemented in a roll-to-roll process to produce alarge number of lighting devices (i.e. final product devicescorresponding to component interconnect boards according to the presentinvention). In a roll-to-roll process, the production facilities areequipped to carry out major parts of the production with sheet materialsfeed by rolls instead of individual sheets. Referring now to FIG. 4,which schematically illustrates a roll-to-roll manufacturing line,including machinery used for patterning, slitting and laminating stepsof the present method. The manufacturing line is here at least partlydescribed with reference to reference numbers and method steps of themethod as described with reference to FIG. 2. However, in theroll-to-roll process, the steps are described with reference to filmsinstead of referring to individual sheets, e.g. conductor sheet 100 ishere referred to as conductor film 100. To continue with reference toFIG. 4, a conductor film 100 is supplied from a feed roll 400 [step1100] into a pattering machine 401, in which a continuous series of thefirst predetermined pattern 115 is punched out or cut out [step 1101].In a parallel process, a patterned resistor film 112 is provided from afeed roll of resistor film 402 fed into a patterning machine 403, inwhich a continuous series of the second predetermined pattern 125 ispunched out or cut out [step 1102]. The patterned conductor film 111 andthe patterned resistor film 112 are then fed into a laminating station404 (e.g. by applying an adhesive and or mechanical pressure and hightemperature) to form the subassembly film 120. The subassembly film 120is subsequently fed into machinery for applying solder [step 1104], pickand placing of components [step 1105], soldering of components [step1106] and mechanical deformation of the subassembly film [steps 1107,1108], e.g. to provide the final circuitry, and form separatesubassemblies 120′ corresponding to respective lighting devices. Here,after the circuitry making is completed, desired substrates 130 areprovided. The substrates may be separate substrates provided on afeeding line after steps of manufacturing including desired deformationetc. [step 1110, not shown in FIG. 2]. The substrates can also beprovided directly from a feed roll.

Decoupling of the manufacturing of the subassembly from the substrate isadvantageous since it allows specific processes to run in their naturalspeeds, and further increases the flexibility of the processingcomponent interconnect boards of different designs in the sameprocessing line.

Further, decoupling of the processing of the subassembly and thesubstrate facilitates for adding or removing optional processing stepsfrom the process line, for instance a 3D shaping of the subassembly maybe removed from the processing if not necessary for a specific componentdesign. Also when changing from one design in factory to another designin factory, if processes are decoupled, it is not longer necessary toexchange tooling for all process steps before machines are made operableagain.

To continue with reference to FIG. 4, finally the subassemblies 120′ andthe substrate 130 are laminated to form final products 150 [step 1109].Optionally, a final process step, e.g. cutting to separate products,applying extra environmental encapsulation etc. may be performed on thefinal products [step 1111].

Machinery utilizing rolling tools are advantageous for their very highspeed performance, and can be used one or more of the different methodsteps, which is indicated by dashed rolls in the steps 1101, 1102, 1107,1108 and 1111 in FIG. 4.

In the steps of the roll-to-roll process as described above, there mightexist a difference in speed for the respective step. In particular, thestep of pick and placing of components [step 1105] is a process stepthat has different processing speed for different designs of thecircuitry. This relatively valuable process step is associated withcostly machines, and may therefore become a bottleneck for the wholemanufacturing line. According to an embodiment of the method (notshown), the pick and placing of components is therefore moved out ofline from the roll-to-roll process as described with reference to FIG.4. This way with every new design the roll-to-roll manufacturing linecan operate at an optimized speed providing for the highest machineutilization factor. The speed may further be variable within a specificdesign. Thereby, different designs of the respective lighting devicescan be created using the same manufacturing line with flexible tooling.Ultimately this means that a manufactured subassembly 120 up to andincluding step 1103 is an intermediate result, which may be created withmultiple designs 120 ^(a), 120 ^(b) etc. These are put on stock tocreate a necessary buffer which is a result of the variable speed ofpick and placing step 1105.

The invention has mainly been described above with reference to a fewembodiments. However, as is readily appreciated by a person skilled inthe art, other embodiments than the ones disclosed above are equallypossible within the scope of the invention, as defined by the appendedclaims.

The invention claimed is:
 1. A method for manufacturing a componentinterconnect board comprising a conductor structure for providingelectrical circuitry to at least one component when mounted on saidcomponent interconnect board, said method comprising: providing apre-cut conductor sheet with a first predetermined pattern; providing apre-cut solder resist sheet with a second predetermined pattern fordefining solder areas of said component interconnect board; forming asubassembly by laminating said pre-cut solder resist sheet on top ofsaid pre-cut conductor sheet; applying solder onto said subassemblyincluding said solder areas; placing said at least one component ontosaid subassembly; performing soldering with said at least one componentonto said subassembly; splitting said subassembly into a plurality ofsubassemblies; and laminating at least one of the subassemblies to asubstrate; wherein, in said subassembly, said solder resist sheet isfurther arranged to act as a carrier for said conductor sheet.
 2. Amethod according to claim 1, further comprising cutting said subassemblyto provide said conductor sheet with a final predetermined patterncorresponding to said conductor structure.
 3. A method according toclaim 1, further comprising providing mechanical deformation of saidsubassembly by means of one of splitting, trimming of the subassembly toa predetermined contour, and stretching.
 4. A method according to claim1, further comprising providing three dimensional deformation of saidsubassembly for providing one of: optical properties, mechanicalfixation of said component interconnect board, mechanical fixation ofadditional components, thermal properties, and connector functionality.5. A method according to claim 1, wherein said substrate is flexible. 6.A method according to claim 1, further providing mechanical deformationof said substrate by means of one of splitting, and trimming of thesubstrate to a predetermined contour.
 7. A method according to claim 1,wherein said conductor structure is further arranged to function as aconnector.
 8. A method according to claim 1, wherein at least one ofsaid first predetermined pattern, and said second predetermined patternis done by means of cutting, punching, or slitting.
 9. A methodaccording to claim 1, performed in a roll-to-roll process.
 10. A methodaccording to claim 1, wherein said first predetermined pattern isprovided with extractable conductor portions.
 11. A method according toclaim 1, wherein said substrate is three dimensional.